In recent years, compact and high performance gyroscopes have been desired for spacecrafts operated in space.
Compact gyroscopes are also desired for navigation systems for automobiles, game machines and cameras.
Coriolis forces, used in gyroscopes, increase when mass and speed of proof masses increase. If smaller proof masses are used to downsize gyroscopes, masses decrease. In order to induce a large Coriolis force with small masses, proof masses have to be moved rapidly. However, the velocity of a proof mass is limited.
Therefore, the prior art gyroscope has the defect that if the gyroscope is downsized, sensitivity and stability are decreased.
FIG. 1 is a figure explaining the Coriolis force. A proof mass 5 having a mass m is connected to a support frame 2 by a support suspension 4. The support suspension 4 is shown by a coil spring. When the proof mass 5 is driven in x-direction at a speed v, and this device is rotated at angular velocity Ω, a Coriolis force Fcori in y-direction is induced.Fcori=2mΩv  (1)
As shown in equation (1), to induce a large Coriolis force, it is necessary to increase the mass m and velocity v of the proof mass 5.
When the proof mass 5 is driven at amplitude x0 and angular frequency ω, the displacement of the proof mass 5 is shown by the equation (2).x=x0 sin(ωt)  (2)
The displacement of the proof mass 5 is differentiated by time, then a velocity v(t) is obtained.V(t)=dx/dt=x0ω cos(ωt)  (3)
Thus, the Coriolis force can be shown as follows.Fcori=2mΩx0ω cos(ωt)  (4)
When only amplitude is considered,Fcori=2mΩx0ω  (5)
Thus, to induce a large Coriolis force, it is necessary to increase the mass m of the proof mass 5, and increase the amplitude and frequency.
In a mechanical oscillation system, the upper limit of driving frequency is resonance frequency of the system. At resonance frequency, it is expected that the amplitude is increased by factor Q. However, the distance that the mass can be moved is limited by the structure of the system, and thus the amplitude does not increase so much.
When the proof mass is driven at the resonance frequency (factor Q), the amplitude is sensitive to fluctuation of frequency, and thus stability is not obtained. Thus, in order to obtain stability, it is better to drive the proof mass at a frequency different from the resonance frequency.
It is assumed that the driving frequency is set to the resonance frequency. It is assumed that a model of a spring-mass system with a lumped constant is used, and spring constant of the suspension 4 is k. Then, the angular frequency ωres is shown as follows.ωres=√(k/m)  (6)
The equation (6) is assigned to the equation (5).Fcori=2mΩx0√(k/m)=2Ωx0√(mk)  (7)
Thus, the Coriolis force is proportional to the amplitude x0, and is proportional to square root of spring constant k and mass m.
In the case of a micro gyroscope including a proof mass 5 with small mass m, when driving force of an actuator for driving the proof mass 5 increases, and the amplitude x0 of the proof mass 5 increases, then a large Coriolis force is induced. That is, the sensitivity of the gyroscope increases. However, the amplitude x0 is limited by the construction of the gyroscope.
Further, like the case when mass m is increased, when spring constant k is increased, a large Coriolis force is induced.
Prior art Patent Publication 1 discloses an oscillating gyroscope which is formed integrally by etching a silicon substrate.
This gyroscope has one oscillator, and a small Coriolis force is induced. Further, this gyroscope is made from one silicon substrate, and thus it is difficult to make a multilayer structure.
Therefore, a more compact and high performance gyroscope is desired, and a fabrication method for making such gyroscope is also desired.
Patent Publication 1: JP H05-209754